Gamma-Delta HSTCL: Post-Allo Relapse + HLH + Dara-Refractory CD38+

Step 0: Immediate Priority - Control the HLH

HLH-Directed Therapy

Step 1: GVL Augmentation - First Move for Post-Allo Relapse

1a. Taper/Withdraw Immunosuppression

• If patient is still on tacrolimus/cyclosporine/MMF, rapid taper is the first intervention
• Risk: triggering or worsening GVHD - in the context of active HLH, this is a major concern
• HLH itself may mimic/mask acute GVHD; clinical judgment essential

1b. Donor Lymphocyte Infusion (DLI)

• Modest but documented activity in T-cell NHL post-allo relapse
• [Dodero et al. - 12 patients with T-cell NHL post-allo relapse received DLI; some durable responses]
• Caveats in this case:
  • Active HLH is a relative contraindication (risk of fulminant GVHD/cytokine storm)
  • Best used AFTER cytoreduction, not in active disease
  • Must debulk first, then DLI as consolidation of any response
  • CD4-selected or low-dose DLI (1x10^6/kg) may reduce GVHD risk

Step 2: Cytoreductive Salvage (Bridge Before DLI or Second Transplant)

For Dara-Refractory CD38+ Disease

• CD2 - expressed (~70%)
• CD7 - expressed (high)
• CD52 - variably expressed (~30-40%)
• CD30 - typically NEGATIVE in HSTCL
• CCR4 - variably expressed
• CD38 - positive but dara-refractory

Preferred Salvage Options (roughly ranked by evidence + biology)

A. Gemcitabine-based regimens

• GemOx (Gemcitabine + Oxaliplatin) or GEMOX ± asparaginase
• Standard go-to for relapsed T-cell NHL; reasonable activity; no cross-resistance with anthracycline/alkylator-based induction
• Less myelosuppressive than platinum-based regimens
• Can be used post-allo with dose reductions

B. Bendamustine

• Single-agent ORR ~50% in PTCL (phase II data)
• Favorable toxicity profile; partial cross-resistance to alkylators only
• Attractive as cytoreduction before DLI in post-allo frail patients
• [Reviewed in post-allo T-cell NHL relapse management guidelines]

C. HDAC Inhibitors (Romidepsin or Belinostat)

• Both FDA-approved for relapsed/refractory PTCL
• Romidepsin: ORR ~25-38% in PTCL (phase II); single-agent activity
• Belinostat: similar ORR ~25%
• Romidepsin has immunomodulatory properties that may augment GVL effects - mechanistically attractive in post-allo setting
• Romidepsin preferred over belinostat in T-cell lymphoma

D. Pralatrexate

• Antifolate; ORR ~29% in PTCL (PROPEL trial)
• Risk of severe mucositis; needs folate/B12 supplementation
• Less favorable in post-allo due to mucosal toxicity

E. Alemtuzumab (anti-CD52)

• Activity if CD52+ (test tumor for expression - often not done in HSTCL)
• ORR 36-50% in relapsed T-cell NHL; not durable as monotherapy
• HIGH risk of opportunistic infections post-allo (profound T-cell depletion)
• Can add profound lymphodepletion which may paradoxically help if DLI is planned after recovery
• Should be used with prophylaxis coverage

F. Nelarabine

• Purine analog; active in T-cell malignancies (approved T-ALL/T-LBL)
• Limited but documented activity in peripheral T-cell lymphoma
• Can combine with alemtuzumab or as single agent
• CNS penetration - relevant if there is concern for CNS involvement

Step 3: Novel/Experimental Options (Particularly Relevant Given Prior Dara Failure)

CD7-Targeted CAR-T Therapy

• This is the most promising experimental option in 2025-2026
• HSTCL expresses CD7 in the majority of cases
• Phase I data (NCT04928105): 5 patients with rare T-cell lymphomas including 1 HSTCL - ORR 80% (3 CR, 1 PR)
• Phase I (NCT05377827): included 2 gamma-delta T-cell lymphoma patients - ORR 80%
• [PMC12653634 - 2025 immunotherapy review for T-cell lymphomas]
• Key challenge: fratricide (CAR-T cells kill each other due to CD7 expression on normal T-cells) - solved by gene editing to knock out CD7 from the CAR-T product
• Best accessed via clinical trial enrollment

PI3K/mTOR Inhibitors

• HSTCL has frequent mutations in PI3K/AKT/mTOR pathway
• Duvelisib (PI3K-delta/gamma inhibitor): approved for T-cell NHL (FDA 2021 for R/R PTCL); ORR 50% in T-PTCL
• Can be used as a bridge strategy; does not appear to impair GVL
• Particularly attractive as an oral, manageable option in post-allo setting

Mogamulizumab (anti-CCR4)

• Approved for CTCL/ATLL; activity in CCR4+ PTCL
• HSTCL variably expresses CCR4 - test for CCR4 expression first
• Post-allo caution: mogamulizumab depletes regulatory T-cells, which can worsen GVHD
• Use with extreme caution if GVHD is a concern

Checkpoint Inhibitors (PD-1/PD-L1)

• Limited data in HSTCL specifically; 1 patient in nivolumab PTCL trial - hyperprogression reported [PMC12653634]
• Hyperprogression is a documented risk in HSTCL with checkpoint inhibition
• Post-allo: risk of severe immune-related adverse events including fatal GVHD
• Generally NOT recommended in this setting

Aurora Kinase Inhibitors (Alisertib)

• Phase I/II data in PTCL - modest activity (ORR ~30% in heavily pre-treated)
• HSTCL molecular features include isochromosome 7q and PI3K pathway dysregulation, not classical aurora kinase dependence
• Lower priority option

Second Allogeneic Transplant

• Feasible if: patient achieves CR/PR with salvage, adequate performance status, no active HLH, no severe GVHD, adequate organ function
• Change donor (haplo from MUD, or different haplo) + different conditioning
• [PMID 36355191 - successful second allo-HSCT with enhanced myeloablative conditioning in refractory HSTCL]
• Only potentially curative option remaining if GVL-based approaches fail
• Timing is critical - must achieve disease control first

Suggested Clinical Approach (Stepwise)

IMMEDIATE (Days 1-7):
├── Stabilize HLH: Dexamethasone + Ruxolitinib ± Anakinra
├── Taper immunosuppression if present
└── Tumor board/transplant team consultation

SHORT-TERM (Week 1-4):
├── Gemcitabine-based OR Bendamustine cytoreduction
├── Add romidepsin if partial response/stable
├── Reassess HLH response
└── Check CD52/CCR4/CD7 expression on tumor

MEDIUM-TERM (1-3 months):
├── If response achieved: DLI from original donor (low dose, CD4-selected)
├── Duvelisib as maintenance bridge
├── Clinical trial enrollment for CD7 CAR-T (strongly recommend)
└── If CR achieved: evaluate second allo-HSCT feasibility

REFRACTORY TO ALL ABOVE:
├── Nelarabine ± alemtuzumab (if CD52+)
├── Emapalumab for HLH if ongoing
└── Best supportive care / palliative pathway discussion

Summary of Key Points

• No standard of care exists - all management is expert opinion/case series level (evidence tier 7-9)
• The combination of post-allo relapse + active HLH + dara-refractory disease represents one of the worst prognostic intersections in lymphoma
• HLH must be controlled simultaneously with lymphoma treatment - use ruxolitinib and/or anakinra + dexamethasone ± etoposide
• Checkpoint inhibitors are likely harmful (hyperprogression risk + GVHD risk post-allo)
• CD7-directed CAR-T is the most biologically rational experimental option - pursue clinical trial access urgently
• Duvelisib (PI3K inhibitor) is the most accessible approved agent with a favorable post-allo safety profile
• DLI remains an important tool but must be deferred until after cytoreduction
• Second allo-SCT with changed conditioning/donor is the only curative option if other measures achieve disease control
• Multidisciplinary discussion at a center with PTCL and transplant expertise is strongly recommended

• [US Multicenter HSTCL-HCT outcomes, Moustafa et al. Transplant Cell Ther 2024 - PMID 38431075]
• [Malignancy-HLH review, Zoref-Lorenz et al. Leuk Lymphoma 2025 - PMID 39656557]
• [Personalized immunotherapy for TCL review, PMC12653634, 2025]
• [Biological agents in secondary HLH review - PMID 42334930, Expert Opin Biol Ther 2026]